A supersonic inlet is a sub-component of an aircraft propulsion system for high speed supersonic aircraft. The supersonic inlet should be designed to efficiently decelerate the approaching high speed airflow to speeds that are compatible with efficient turbojet engine operation and to provide optimum matching of inlet and engine airflow requirements. Entrance airflow speeds to existing airbreathing engines must be subsonic; therefore, it is necessary to decelerate the airflow speed during supersonic flight. Typically, engine entrance Mach numbers for supersonic propulsion systems are 0.3 to 0.4. The inlet must reduce the velocity of the approaching airflow to these subsonic levels while maintaining a minimum of loss in freestream total pressure and while maintaining a near uniform flow profile at the engine entrance. In addition, it is essential that the inlet diffuse the air in a manner to minimize the pressure losses, cowl and additive drag, and flow distortion.
Prior art mixed compression inlets designed for supersonic cruise conditions have not been able to achieve high performance, reduced weight and mechanical complexity, as well as supply the large amount of engine airflow required for transonic conditions and takeoff conditions. The inlet must also have a wide range of operability where safety is an important consideration in order to ensure that the inlet will absorb airflow disturbances that can trigger an inlet unstart, which is a potentially dangerous condition which occurs when the normal shock moves out of the inlet duct to a position upstream of the cowl lip, and results in a rapid decrease in flight speed and engine power. Thus prior art inlets have generally traded off one or more important performance parameters at the expense of another. For example, the traditional "translating centerbody" (TCB) axisymmetric inlet has a narrow operability margin and is limited in its transonic airflow capability. Another type of mixed compression inlet known as the "variable diameter axisymmetric centerbody" (VDC) inlet is very mechanically complex and may result in high maintenance or manufacturing costs. A third type of mixed compression inlet referred to as a "two-dimensional" (2D) inlet is heavy and may impose an integration drag penalty when compared to the axisymmetric designs.
Thus it is desired to have a new and improved inlet design which provides the high performance, required transonic airflow, while maintaining an acceptable operability margin for external disturbances.